RF Transistor Noise Source
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From: RST Engineering on 28 Dec 2009 16:49 .. .. There was a general discussion in this NG a couple of weeks ago about using a lightly-biased zener as a noise source. There was no clear definition about how flat or to what frequency the noise was useful. It got me to thinking and I'll do the experiment as soon as I can clean off my bench, but what do you think I'm going to see for reasonable noise bandwidth if I use a small signal (like a 2N5770 or 918) and use the emitter-base junction as the zener. Most of them zener somewhere around 5 volts and that should be reasonable. Most of the comments regarding bandwidth using a "regular" zener centered around the rather large junction area necessary to carry some decent current; the junction of an RF transistor ought to be at least an order of magnitude (several??) smaller than that. Thoughts? Jim
From: Tim Wescott on 28 Dec 2009 17:07 On Mon, 28 Dec 2009 13:49:05 -0800, RST Engineering wrote: > . > . > There was a general discussion in this NG a couple of weeks ago about > using a lightly-biased zener as a noise source. There was no clear > definition about how flat or to what frequency the noise was useful. > > It got me to thinking and I'll do the experiment as soon as I can clean > off my bench, but what do you think I'm going to see for reasonable > noise bandwidth if I use a small signal (like a 2N5770 or 918) and use > the emitter-base junction as the zener. Most of them zener somewhere > around 5 volts and that should be reasonable. > > Most of the comments regarding bandwidth using a "regular" zener > centered around the rather large junction area necessary to carry some > decent current; the junction of an RF transistor ought to be at least an > order of magnitude (several??) smaller than that. > > Thoughts? It'll be good to know what your results are. Twenty years ago you could buy a noise diode from MA-COM (IIRC; it may have been some other company), home-brew your own circuit to hold it, then send it back to MA-COM for calibration. I don't know if you still can. A noise diode was, of course, 'just a zener', optimized for use at microwave frequencies. -- www.wescottdesign.com
From: RST Engineering on 28 Dec 2009 17:49 On Mon, 28 Dec 2009 16:07:24 -0600, Tim Wescott <tim(a)seemywebsite.com> wrote: >On Mon, 28 Dec 2009 13:49:05 -0800, RST Engineering wrote: > >It'll be good to know what your results are. > >Twenty years ago you could buy a noise diode from MA-COM (IIRC; it may >have been some other company), home-brew your own circuit to hold it, >then send it back to MA-COM for calibration. I don't know if you still >can. > >A noise diode was, of course, 'just a zener', optimized for use at >microwave frequencies. Noisecom and Micronetics are the only two I know of. Noisecom used to sell "factory seconds" to hams for pennies on the dollar but that practice seems to have gone by the wayside. They, as you noted, would also do a calibration of your design for a few bucks. Gone also. It will be fun to get back to experimenting with something where I don't have a real good idea what the answer is going to be. Jim
From: Tim Wescott on 28 Dec 2009 18:59 On Mon, 28 Dec 2009 14:49:06 -0800, RST Engineering wrote: > On Mon, 28 Dec 2009 16:07:24 -0600, Tim Wescott <tim(a)seemywebsite.com> > wrote: > >>On Mon, 28 Dec 2009 13:49:05 -0800, RST Engineering wrote: > > >>It'll be good to know what your results are. >> >>Twenty years ago you could buy a noise diode from MA-COM (IIRC; it may >>have been some other company), home-brew your own circuit to hold it, >>then send it back to MA-COM for calibration. I don't know if you still >>can. >> >>A noise diode was, of course, 'just a zener', optimized for use at >>microwave frequencies. > > Noisecom and Micronetics are the only two I know of. Noisecom used to > sell "factory seconds" to hams for pennies on the dollar but that > practice seems to have gone by the wayside. They, as you noted, would > also do a calibration of your design for a few bucks. Gone also. > > It will be fun to get back to experimenting with something where I don't > have a real good idea what the answer is going to be. > > Jim I think it's Noisecom that I was thinking of. Dang; I should have taken advantage while I could. I have thought that if you were building something low-noise enough you could measure the noise figure with a pair of transmission lines terminated in resistors: drop one into ice water (or dry-ice/acetone, or LN2), and heat the other one up (boiling water, or a not-quite-melted- solder heat furnace). Then switch between them. With no current flowing through the resistors, you'd certainly know their noise temperatures! -- www.wescottdesign.com
From: Phil Hobbs on 28 Dec 2009 19:08
On 12/28/2009 6:59 PM, Tim Wescott wrote: > On Mon, 28 Dec 2009 14:49:06 -0800, RST Engineering wrote: > >> On Mon, 28 Dec 2009 16:07:24 -0600, Tim Wescott<tim(a)seemywebsite.com> >> wrote: >> >>> On Mon, 28 Dec 2009 13:49:05 -0800, RST Engineering wrote: >> >> >>> It'll be good to know what your results are. >>> >>> Twenty years ago you could buy a noise diode from MA-COM (IIRC; it may >>> have been some other company), home-brew your own circuit to hold it, >>> then send it back to MA-COM for calibration. I don't know if you still >>> can. >>> >>> A noise diode was, of course, 'just a zener', optimized for use at >>> microwave frequencies. >> >> Noisecom and Micronetics are the only two I know of. Noisecom used to >> sell "factory seconds" to hams for pennies on the dollar but that >> practice seems to have gone by the wayside. They, as you noted, would >> also do a calibration of your design for a few bucks. Gone also. >> >> It will be fun to get back to experimenting with something where I don't >> have a real good idea what the answer is going to be. >> >> Jim > > I think it's Noisecom that I was thinking of. Dang; I should have taken > advantage while I could. > > I have thought that if you were building something low-noise enough you > could measure the noise figure with a pair of transmission lines > terminated in resistors: drop one into ice water (or dry-ice/acetone, or > LN2), and heat the other one up (boiling water, or a not-quite-melted- > solder heat furnace). Then switch between them. With no current flowing > through the resistors, you'd certainly know their noise temperatures! > A common approach in physics labs is to terminate the input with a 300 kelvin resistor, measure the noise, dunk the resistor in liquid nitrogen, and measure it again. Works great. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 email: hobbs at electrooptical dot net http://electrooptical.net |